Photosynthesis: Discovery!

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Objective

Students will be able to discover basic ideas about photosynthesis.

Big Idea

Where does the mass of a tree come from?

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Purpose of Lesson:

 The purpose of this lesson is to introduce the concept of photosynthesis to the class, gather information about prior knowledge that the students have, and provide connections with real life.

 

Major Strategies to Watch for:

1. Self assessed discussion strategy using sentence starters to ensure depth and participation. 

2. Circle Map for Brainstorming and Evaluation of strength of conviction.

3. Frayer model for understanding a concept at a deep level.  

Ready. Set. Engage!

5 minutes

Learning Goal: Discover how photosynthesis plays a role in our lives.

Opening Question: Where does the mass of a tree come from? 

Students record their opening question on their learning goal sheet and are ready to start class 3 min after the bell has rung.  I reward students who get started early with ROCK STAR SCIENTIST tickets.  

Follow the links to learn more about the beginning of class strategies and ROCK STAR scientist tickets.   

Pre-Assessment

5 minutes

I start each unit with a pre-assessment to open up the student thinking and help uncover misconceptions. This allows be to modify my teaching, compact curriculum, form appropriate groups, and measure growth. By far the best formative probes I've found are by Page Keeley. She's written several books of probes including Uncovering Student Ideas in Science Volume 1, 2, 3 and 4. 

These two probes, "Giant Sequoia Tree," and "Plants in the Dark and Light," are to elicit student understanding of photosynthesis and sunlight.  I generally don't do both of the probes on the same day, but I'm putting them both in this section to show two different probes that could be used to tease out ideas.  

In "Plants in the Dark and Light," students are given a situation with a plant that is put in the light and another one put in the dark.  Students are asked to choose between four statements that predict the outcome of the experiment.  Then students are asked to explain their thinking. This probe will indicate whether students are connecting sunlight with growth.  In the student response, the student's answer indicates that they have correctly connected plant growth with sun.

In "Giant Sequoia Tree" the students are asked to decide what makes up the wood and leaves matter, listing items for students to choose from. This probe uncovers whether students understand that the mass of the tree comes from the carbon dioxide in the air. 

In the student response, she choose the answer sunlight, indicated several misconceptions. She might think that sunlight has mass and cannot yet identify mass and energy. Also, she did not choose any other items.

These responses tell me that the students are not ready for this material to be compacted and while they have a strong connection with photosynthesis and sunlight, there is work to be done on the concept of matter, mass, and chemical reactions.

Hook

15 minutes

The purpose of this section is to get students interested in learning the subject.  This is especially important for topics like photosynthesis because it has a "sciency" name AND students already think they know it!  

For this opening I ask the students to discus photosynthesis using our sentence starters,

  • I think...
  • I agree because...
  • I disagree because...
  • I want to add on...
  • This connects with...

I walk around listening to the discussions and prompting students to use the sentence starters.

After we have had the discussion, I show this video.  

I like to stop this video at different points to emphasize certain aspects.  For example, I'll stop the video after the narrator proves that the mass could not come from the soil. I ask the kids to raise their hand if that was their prediction and then ask them to make a new prediction.  In this way, genuine engagement builds throughout the video until the students are begging to know where the mass of the tree came from.

Discovery Activity

15 minutes

The purpose of this section is to pre-assess student knowledge and to give all students an understanding of the word "Photosynthesis."  

I like to do this using a Circle map. This is a Thinking Map, designed to help students brainstorm within a framework.  I have students draw a circle in their notebooks. Then they put in everything they know or think they know about photosynthesis. I ask students to put an exclamation mark by items they are very sure about, a period by items they are comfortable with and a question mark by items that are guesses. This is a wonderful way to not only get student information but also quickly get how solidly the students are holding onto ideas.  It also gives permission for students to put down their guesses. This is essential for perfectionists who often won't write anything down if they aren't 100% sure of it.

This is a circle drawing showing student thinking. I was surprised by the items the students put down. In particular, it seemed clear that this student had a passion for learning about the ocean and was making all sorts of connections that were interesting.

Once we have done the circle maps and shared them with our partners, I ask students to take a note card and get ready to make a Frayer Model. Even though this is not the first Frayer Model we have made, I still make a picture on the board. 

Below is a screencast of how I teach a Frayer Model. This is not the first Frayer Model of the year, so I wouldn't necessarily do a full focus lesson. But if students are struggling, it would be worth adding in some modeling.  

 

Students then work with me to make the Frayer for Photosynthesis. Generally, I guide the thinking on the definition and the characteristics and let students guide the thinking on the examples and the non-examples. This ensures that students have the right information on their resource while still opening the class up to collaborative discussion.  

At the end of the class students hand in their Frayer Models as a piece of evidence of understanding. They also make a wonderful display in the classroom!

Discussion

10 minutes

The purpose of this section is to try to make the learning personal to the students.  

I ask this question, "Now that we remember the word photosynthesis and have seen a video about photosynthesis, how does photosynthesis relate to you? Why are we studying this?

Again, we use the sentence starters;

  • I think...
  • I agree because...
  • I disagree because...
  • I want to add on...
  • This connects with...

When students are done, I have them self assess their discussion using our checklist.

_____ I stayed on topic

_____ I used the sentence starters.

_____ I listened and responded to my partner.

_____ I made connections to the real world.

The students record their score on their Student Learning Trackers.

When we have done that, I poll a few students to find out why they think photosynthesis is important to them.  After listening to all the answers I make sure to make the point, "If you ate food today...then you relied on photosynthesis.  So if eating is important to you, you should care about this process."  

Closure

2 minutes

 Closing Statement: "We have started understand the concept of photosynthesis.  I hope when you look around at trees today you have some new thoughts about where they come from."

Closing Question: "Why do you think it is so surprising to think that most of the mass of a tree comes from carbon dioxide?"


Closure depends greatly on timing and is not as easy to plan in advance as opening.  You can find more information about how I manage closure here.